The present invention relates to a winch over-winding prevention apparatus that stops the upward hoisting motion of a suspended object such as a hook in the operation of, for instance, a crane operation machine.
Hook over-winding prevention apparatuses in the prior art that stop the drive of a winch by detecting an over-wind of a hook include that disclosed in Japanese Utility Model Registration No. 2552639. This over-winding prevention apparatus is provided with a stop switch, which is turned on when the hook is wound up by a distance equal to or more than a specific distance, at the front end of the boom and unloads hydraulic fluid from the hydraulic pump as the stop switch is turned on. The supply of the pressure oil from the hydraulic pump to the hydraulic motor is suspended, to stop the drive of the winch.
Today, winches are driven at higher speeds than ever before, and thus, there arises a problem in that when the hook over-winding prevention apparatus operates during a fast upward hoisting operation, the suspended object, such as a hook, swings upward due to its inertial force, to result in damage to parts caused by the impact load applied to a supporting member such as a boom by the swinging object, which may even come into contact with the front end of the boom. In order to prevent the hook from coming into contact with the boom during a fast upward hoisting operation, it is necessary to provide the stop switch at a position that is lower than the boom front end to anticipate the upward swing of the suspended object. In such a case, however, the operating range of the hoist operation becomes limited.
In order to address this problem, the apparatus disclosed in the publication mentioned above is further provided with a speed limiting switch at a position lower than that of the stop switch to limit the quantity of hydraulic fluid supplied from the hydraulic pump to the hydraulic motor by reducing the area of the oil passage for the hydraulic fluid (fixed orifice) when the speed limiting switch is turned on. As a result, the winch drive speed is reduced, and even when the hook over-winding prevention apparatus subsequently operates as the stop switch is turned on, the suspended object does not swing upward to a great degree and the upward hoist motion of the hook is immediately stopped.
However, in the apparatus disclosed in the publication, the position at which the speed reduction starts is determined in correspondence to the position at which the speed limiting switch is mounted and the ratio of the speed reduction (deceleration) is determined by the degree of the fixed orifice, bearing no relation to the hoist speed. Thus, if the speed reduction start position and the speed reduction ratio are set in correspondence to a high hoist speed, the speed reduction starts too early when the hoist operation is performed at low speed, to result in poor work efficiency. If, on the other hand, the speed reduction start position and the speed reduction ratio are set in correspondence to a low hoist speed, the speed reduction starts too late when the hoisting operation is performed at high speed, to induce the problem discussed earlier of the upward swing of the suspended object.
An object of the present invention is to provide a winch over-winding prevention apparatus that is capable of stopping a hoist operation of a suspended load with optimal timing without inducing poor work efficiency or upward swing of the suspended object.
In order to attain the above object, a winch over-winding prevention apparatus according to the present invention comprises: a winch drum that is driven for up/down hoist in response to a command issued through an operating lever; a stop switch that is activated when a suspended object raised or lowered as a hoisting cable wound around the winch drum is further taken up or fed out is hoisted up to a predetermined stop position; and a stop device that stops drive of the winch drum when the stop switch is activated, and further comprises: a speed detection device that detects a hoist speed of the suspended object; a speed reduction device that reduces a drive speed of the winch drum once the suspended object reaches a predetermined speed reduction start position; and a speed reduction control device that calculates a deceleration rate of the winch drum in correspondence to the hoist speed of the suspended object detected by the speed detection device and controls drive of the speed reduction device in response to a speed reduction command corresponding to the deceleration rate.
In this winch over-winding prevention apparatus, it is preferred that the speed reduction control device calculates the deceleration rate so as to set the drive speed of the winch drum immediately prior to a stop at the predetermined stop position to a predetermined speed regardless of the hoist speed detected by the speed detection device. Furthermore, it is preferred that the speed reduction control device calculates the deceleration rate so as to set the drive speed of the winch drum to the predetermined speed at a speed reduction end position set between the speed reduction start position and the predetermined stop position, and controls the drive of the speed reduction device by outputting a speed reduction command corresponding to the deceleration rate until the suspended object having departed the speed reduction start position reaches the speed reduction end position and outputting a constant speed command corresponding to the predetermined speed until the suspended object having departed the speed reduction end position reaches the stop position.
Another winch over-winding prevention apparatus comprises: a winch drum that is driven for up/down hoist in response to a command issued through an operating lever; a stop switch that is activated when a suspended object raised or lowered as a hoisting cable wound around the winch drum is further taken up or fed out is hoisted up to a predetermined stop position; and a stop device that stops drive of the winch drum when the stop switch is activated, and further comprises: a speed detection device that detects a hoist speed of the suspended object; a position detection device that outputs a signal corresponding to a raised or lowered position of the suspended object; a speed reduction device that reduces a drive speed of the winch drum; and a speed reduction control device that calculates a speed reduction start position in correspondence to the hoist speed of the suspended object detected by the speed detection device and controls drive of the speed reduction device by outputting a predetermined speed reduction command when the suspended object is detected to have reached the speed reduction start position through a signal output by the position detection device.
In this winch over-winding prevention apparatus, it is preferred that the speed reduction control device outputs a speed reduction command to reduce the drive speed of the winch drum at a constant deceleration rate and calculates the speed reduction start position so as to set the drive speed of the winch drum immediately prior to a stop at the predetermined stop position to a predetermined speed. Furthermore, it is preferred that the speed reduction control device calculates the speed reduction start position so as to set the drive speed of the winch drum to the predetermined speed at a speed reduction end position set between the speed reduction start position and the predetermined stop position, and controls the drive of the speed reduction device by outputting a speed reduction command corresponding to the predetermined deceleration rate until the suspended object having departed the speed reduction start position reaches the speed reduction end position and outputting a constant speed command corresponding to the predetermined speed until the suspended object having departed the speed reduction end position reaches the stop position.
Also, in this winch over-winding prevention apparatus, it is preferred that the speed reduction control device also calculates a deceleration rate of the winch drum in correspondence to the hoist speed of the suspended object detected by the speed detection device and controls the drive of the speed reduction device by outputting a speed reduction command corresponding to the deceleration rate when the suspended object is detected to have reached the speed reduction start position through a signal output by the position detection device.
Another winch over-winding prevention apparatus comprises: a winch drum that is driven for up/down hoist in response to a command issued through an operating lever; a stop switch that is activated when a suspended object raised or lowered as a hoisting cable wound around the winch drum is further taken up or fed out is hoisted up to predetermined stop position; and a stop device that stops drive of the winch drum when the stop switch is activated, and further comprises: a speed reduction device that reduces a drive speed of the winch drum once the suspended object reaches a predetermined speed reduction start position; and a speed reduction control device that controls drive of the speed reduction device by outputting a speed reduction command until the suspended object having departed the speed reduction start position reaches a predetermined speed reduction end position and outputting a constant speed command until the suspended object having departed the speed reduction end position reaches the stop position.
In each of the above winch over-winding prevention apparatuses, it is preferred that the speed reduction device controls a physical quantity bearing a correlation to a motor rotation rate of a hydraulic motor that drives a winch drum; and the speed reduction control device resets an output of the speed reduction command when the operating lever is driven for a hoist-down.
In each of the above winch over-winding prevention apparatuses, it is preferred that the stop device is provided with a negative brake device that stops drive of the winch drum.
Another winch over-winding prevention apparatus comprises: a winch drum that is driven for up/down hoist in response to a command issued through an operating lever; a stop switch that is activated when a suspended object raised or lowered as a hoisting cable wound around the winch drum is further taken up or fed out is hoisted up to a predetermined stop position; and a stop device that stops drive of the winch drum when the stop switch is activated, and further comprises: a position detection device that outputs a signal corresponding to a raised or lowered position of the suspended object; a speed reduction device that reduces a drive speed of the winch drum; and a speed reduction control device that controls drive of the speed reduction device by outputting a predetermined speed reduction command when the position detection device detects a speed reduction start position set in correspondence to a predetermined maximum hoist speed for the suspended object.
In this winch over-winding prevention apparatus, it is preferred that the speed reduction control device outputs a speed reduction command to reduce the drive speed of the winch drum at a constant deceleration rate and sets the speed reduction start position so as to set the drive speed of the winch drum immediately prior to a stop at the predetermined stop position to a predetermined speed.
As explained above, since the speed of the winch drum is reduced at a deceleration rate corresponding to the speed with which the suspended object is being hoisted and the speed reduction start position is changed in correspondence to the speed at which the suspended object is being hoisted, the hoist speed immediately before a stop can be set at a specific low speed regardless of the hoist speed immediately before the speed reduction. As a result, the suspended load can be stopped with the optimal timing corresponding to the hoist speed. In addition, the work efficiency is not compromised and no upward swing of the suspended object is induced. Furthermore, since the execution of the speed reduction command is completed before the suspended object reaches the stop position and the winch is driven at a constant speed, the winch is driven at a specific speed set to ensure that the winch at the stop position remains unaffected by any adverse factors such as an assembly error and then is stopped. Moreover, the winch drum is slowed down by outputting a specific speed reduction command when the position detection device detects the speed reduction start position set in correspondence to the specific maximum suspended object hoist speed, it is not necessary to detect the hoist speed of the suspended object, thereby achieving structural simplicity.